Acute massive pulmonary embolus is generally associated with a high mortality. The present proposal seeks to determine if extra corporeal membrane lung oxygenation can be utilized as a method of support during the critical period of cardiopulmonary failure following massive embolization. Adult baboons will be given fatal massive pulmonary emboli and then supported on membrane lung bypass for varying periods. Any hematologic alterations associated with long-term perfusion will be measured. In addition, the efficacy of venoarterial support in improving cardiopulmonary hemodynamics will be determined.